DS,
You wrote,[...how long...depression..away?..?].
It depends. There are different kinds of depression that have different causes. These differnt causes have time periods associated with other factors that can determine the length of the depression. Some depressions could be idiopathic, so the term could be unknown. I have found many causes for depression, and if you could identify your cause, then I could offer support from my perspective if you would like.
Lou